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<p dir="ltr">Due to the vast increase and versatility of Additive Manufacturing and 3D-printing, in this study, the mechanical behavior of implementing both continuous and short carbon fiber within Nylon and investigated for its effectiveness within additively manufactured prints. Here, 0.1wt% of pure nylon was combined with carbon nanotubes through both dry and heat mixing to determine the best method and used to create printable filaments. Compression, tensile and short beam shear (SBS) samples were created and tested to determine maximum deformation and were simulated using ANSYS and its ACP Pre tool. SEM imaging was used to analyze CNT integration within the nylon filament, as well as the fractography of tested samples. Experimental testing shows that compressive strength increased by 28%, and the average SBS samples increased by 8% with minimal impacts on the tensile strength. The simulated results for Nylon/CF tensile samples were compared to experimental results and showed that lower amounts of carbon fiber samples tend to have lower errors.</p>

<p>With the emergence of additive manufacturing (AM), there is a need to understand the role of microstructures resulting from AM on the mechanical performance of the material. Ti-6Al-4V alloys are widely used within the aerospace industry as well as other industries to achieve high strength, low weight premium performance parts. There is a desire to utilize AM to produce Ti-6Al-4V, although these materials need to be qualified prior to their use in safety critical applications. Within the qualification of AM Ti-6Al-4V in aeronautics, fatigue loading is a crucial aspect to. It has been seen that within AM Ti-6Al-4V, prior β boundaries can be locations of microscopic localization of plastic strain which often lead to fatigue crack initiation. This thesis aims to further understand and predict the role of AM Ti-6Al-4V microstructures in dictating fatigue behavior. Specifically, the goal was to gauge the contributions of two microstructural features resulting from AM, prior β boundaries and α lathe-shaped grains, to the localization behavior. With the need to understand and predict the emergent behavior of the material system, crystal plasticity finite element (CPFE) methods were used in this thesis as the main method. </p> <p><br></p> <p>Within the context of CPFE, there is an existing gap in the current literature of realistic synthetic microstructures of Ti-6Al-4V that capture both the prior β boundaries and α lathes. With the ability to generate realistic FE models, the effects of the microstructural features can be better studied and characterized. The first portion of this thesis focuses on the generation of such synthetic microstructures which are simulated within the CPFE framework. An emphasis is placed on modeling the prior β boundaries and α grains. As these generated models are statistically equivalent to actual microstructures, material characterization via EBSD was performed on specimen that were used in the experimental fatigue testing. With the framework’s ability to generate synthetic microstructures that consider one prior β grain or multiple β grains (and thus prior β boundaries), simulations were conducted on both conditions of microstructures. </p> <p><br></p> <p>In the second portion of this thesis, simulations are conducted on two conditions of synthetic microstructures: models which contain 𝛼 lathes associated with one prior 𝛽 grain and models which contain multiple prior 𝛽 boundaries and the respective 𝛼 lathes. The goals of the simulations included: (1) lifing the different synthetic microstructures using a fatigue lifing model by way of the accumulated plastic strain energy density (APSED), (2) analyzing the microscopic localization of APSED at the prior β boundaries, and (3) analyzing the effects of the α lathes on the microscopic localization. This investigation aimed to further shed light on the effects of the additive manufacturing process and the implications of the resulting microstructure on the fatigue properties of AM Ti-6Al-4V. Furthermore, physics-based prognosis strategies similar to what is employed here will enable the rapid qualification of materials/structures and the ability to tailor component design on fatigue performance. </p>

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<p dir="ltr">I conducted an in-depth analysis of the frequency and severity of external load accidents involving Chinook helicopters over a period of 30 years. The literature review encompassed General Aviation (GA) and ground-based safety organizations, while the data analysis predominantly relied on secondary data from the Army Combat Readiness Center (ACRC). In conducting this study, I aimed to identify key trends, causes, and effects of these accidents, particularly emphasizing material failures, human errors, and the substantial impact of rotor downwash as horizontal wind velocities in proximity to the ground. The study's goal was to improve safety and operational efficiency in Chinook external load operations by identifying frequency and severity of accidents over a 30-year period. The hope was that this would provide valuable insights for improvements in risk mitigation techniques.</p><p dir="ltr">By using an exploratory secondary data analysis of both publicly available U.S. Army accidents and accident data provided by the U.S. ACRC, I found that Chinook rotor downwash, which manifests as horizontal wind velocity when in close proximity to the ground, is the most significant and underreported factor. Based on the findings of this research, I recommend improved classification and documentation of such accidents. The findings highlighted the urgency of updating training and operational procedures to effectively address the unique challenges posed by rotor downwash and high gross weights in proximity to the ground, typical of Chinook external load Pickup and Landing Zone (PZ/LZ) operations. Implementing these recommendations is expected to enhance safety measures in both training and practical operations, ultimately reducing future accidents and improving safety standards in the aviation industry.</p>

<p dir="ltr">This work focuses on the fracture behavior and failure mechanisms of Prepreg Platelet Molded Composites (PPMCs), which are characterized by meso-structural variability. The study investigates the interlaminar fracture toughness of PPMCs using both experimental and computational approaches, with a particular focus on Mode-I fracture testing. Cohesive zone models are developed to simulate interfacial behavior in composite laminates. The research introduces the concept of the platelet critical length problem and explores how platelet geometry, arrangement, and meso-structural features affect fracture toughness and energy absorption. Findings indicate that smaller platelets enhance fracture toughness through mechanisms like platelet bridging and crack deflection, while larger platelets provide more consistent fracture properties but exhibit greater variability in stiffness. This work offers valuable insights for optimizing PPMC performance in high-performance applications.</p>

<p dir="ltr">This thesis investigates nonlinear dynamical systems through a transdisciplinary lens, addressing three critical domains impacting human well-being: environmental pollution, climate migration and gender dynamics, and public health security. These are environmental induced challenges that impact health and social stability. These domains exhibit nonlinear characteristics that require adaptive, sustainable solutions beyond traditional linear approaches. Utilizing the Adaptive Pathways Framework (APF), this research integrates multi-scale fluid dynamics, engineering design, applied mathematics, and social science insights to create resilient models aligned with the United Nations Sustainable Development Goals (UNSDGs). The first focus area, aeroacoustic noise in urban air mobility, explores bio-inspired metamaterials for passive noise control. Periodic and quasi-periodic micropillar arrays inspired by sharkskin demonstrate significant noise reduction, contributing to quieter and more sustainable urban environments. The second area addresses climate migration, applying dimensional analysis from fluid dynamics to model migration patterns influenced by environmental, social, and economic factors. This framework offers policymakers quantitative tools for climate adaptation strategies. The third area centers on refugee empowerment, focusing on gender-targeted interventions that integrate STEM education and entrepreneurship to support social integration. This work provides scalable pathways for empowering refugee women and fostering resilience within refugee communities. The fourth area addresses gender equity in STEM, employing nudge theory and design thinking to challenge biases and create a more inclusive environment. Behavioral interventions here offer strategies for sustainable change in scientific research practices. Finally, the fifth area, public health security, explores sustainable innovations for pandemic resilience, including virus filtration and electrostatic disinfection technologies, balancing immediate health needs with long-term environmental considerations. This thesis underscores the efficacy of transdisciplinary approaches in tackling complex, nonlinear challenges, promoting sustainable, adaptive outcomes for global environmental, social, gender, and health stability.</p>

<p dir="ltr">The increasing use of additive manufacturing technologies such as Laser Powder Bed Fusion (LPBF) has enabled the manufacturing of parts with complex features such as optimized cooling channels. However, due to the layer-by-layer deposition of LPBF requiring an approximation of design intent, cooling channels manufactured by LPBF are affected by surface roughness effects and manufacturing inaccuracies. Consequently, the effect of implementing them on the mechanical properties of parts should be studied to understand their limits of applicability. This study aims to determine the effect of helical cooling channels in LPBF GRCop-42 specimens on their high-cycle fatigue properties. We present monotonic tensile testing and high-cycle fatigue testing results for three specimen types (no channel, straight channel and helical channel) of LPBF GRCop-42 under uniaxial loading, tested at two temperature conditions (room and 500°C). We show that at room temperature, the no channel specimens had the highest fatigue strength, followed by the straight channel and then helical channel specimens. The relative significance of potential causes for the detriment in fatigue life for the straight and helical channeled specimens were quantified using finite element analysis (FEA) and analytical fatigue models (based on Murakami-type defect corrections), and the findings from this analysis were validated by experimental observations from fracture surface analysis. Our results demonstrate that for the straight channel specimens, manufacturing-induced porosity around the channel is relatively a stronger driver for the detriment of fatigue life, compared to surface roughness. For the helical channel specimens, intended to simulate complex cooling channels in real-world applications, the effects of surface roughness combined with multiaxial stress concentrations around the channel were the primary driver for the lesser fatigue life. We anticipate our results will be useful for designers and manufacturers of LPBF components with complex features, and those involved in the potential implementation of LPBF GRCop-42 parts in high-cycle fatigue applications.</p>